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排序方式: 共有498条查询结果,搜索用时 31 毫秒
1.
Bahattin Gümgüm Nermin Biricik Feyyaz Durap Ismail Özdemir Nevin Gürbüz Wee Han Ang Paul J. Dyson 《应用有机金属化学》2007,21(8):711-715
Palladium(II) complexes with N,N‐bis(diphenylphosphino)aniline ligands catalyse the Heck reaction between styrene and aryl bromides, affording stilbenes in good yield. The structures of two of the complexes used as pre‐catalysts have been determined by single‐crystal X‐ray diffraction. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
2.
The classical economic order quantity (EOQ) model assumes that items produced are of perfect quality and that the unit cost of production is independent of demand. However, in realistic situations, product quality is never perfect, but is directly affected by the reliability of the production process. In this paper, we consider an EOQ model with imperfect production process and the unit production cost is directly related to process reliability and inversely related to the demand rate. In addition, a numerical example is given to illustrate the developed model. Sensitivity analysis is also performed and discussed. 相似文献
3.
This paper studies the tail behavior of the fundamental period in the MAP/G/1 queue. We prove that if the service time distribution
has a regularly varying tail, then the fundamental period distribution in the MAP/G/1 queue has also regularly varying tail,
and vice versa, by finding an explicit expression for the asymptotics of the tail of the fundamental period in terms of the
tail of the service time distribution. Our main result with the matrix analytic proof is a natural extension of the result
in (de Meyer and Teugels, J. Appl. Probab. 17: 802–813, 1980) on the M/G/1 queue where techniques rely heavily on analytic expressions of relevant functions.
I.-S. Wee’s research was supported by the Korea Research Foundation Grant KRF 2003-070-00008. 相似文献
4.
This study examines the dependence of the sputter rate and the transient width (ztr) as a function of Cs+ primary ion energy (impact energy (Ep) = 320 eV, 500 eV and 1 keV) and incident angles between 0 and 70° . The instrument used was the ATOMIKA 4500 SIMS depth profiler and the sample was Si with ten delta layers of Si0.7 Ge0.3. We observed the narrowest transient widths of between 1.4 and 2.0 nm apparent depth. This was achieved at incident angles (θ) of 30–50° . An extended transient effect was observed when profiled at θ > 50° . Below this incident angle, the transient width is less than twice the penetration depth (ztr < 2Rnorm). At minimum ztr, ztr ≈ Rnorm. The detection sensitivity is best achieved at θ ≈ 30° for all energies investigated. The sputter rate is lowest at normal incidence, rising gradually to a maximum at θ ≈ 50–60° . This is similar to that observed with ultralow‐energy O2+ primary ion beams. 1 At ultralow energies, reducing Ep does not have a significant effect in reducing ztr. We conclude that for Ep < 1 keV, the optimum condition to achieve minimum ztr while maintaining good sensitivity and high sputter rate is at θ ≈ 30° . Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
5.
K. W. Cheah L. C. Ho J. B. Xia J. Li W. H. Zheng W. R. Zhuang Q. M. Wang 《Applied Physics A: Materials Science & Processing》1995,60(6):601-606
Photoluminescence studies on porous silicon show that there are luminescence centers present in the surface states. By taking photoluminescence spectra of porous silicon with respect to temperature, a distinct peak can be observed in the temperature range 100–150 K. Both linear and nonlinear relationships were observed between excitation laser power and the photoluminescence intensity within this temperature range. In addition, there was a tendency for the photoluminescence peak to red shift at low temperature as well as at low excitation power. This is interpreted as indicating that the lower energy transition becomes dominant at low temperature and excitation power. The presence of these luminescence centers can be explained in terms of porous silicon as a mixture of silicon clusters and wires in which quantum confinement along with surface passivation would cause a mixing of andX band structure between the surface states and the bulk. This mixing would allow the formation of luminescence centers. 相似文献
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8.
Ln(Ln=Y/Gd)VO4:Er3+/Nd3+的制备及发光性能 总被引:2,自引:0,他引:2
采用高温固相法制备了Ln(Ln=Y/Gd)VO4掺Er^3+或Nd^3+的近红外发光材料。通过X射线粉末衍射(XRD)和光致发光(PL)对样品进行了表征。结果表明:所得产品结晶良好,属于四方晶系,锆石结构。研究了Er^3+,Nd^3+的含量、煅烧时间、煅烧温度等对材料近红外发光性质的影响。在Ln(Ln=Y/Gd)VO4:Er^3+/Nd^3+中,存在明显的从VO4^3-向Er^3+/Nd^3+的能量传递。两种不同的LnVO4(Ln=Y/Gd)基质对发光性质也有一定的影响。小浓度Bi^3+的掺人可以明显提高YVO4:Er^3+/Nd^3+的近红外发光强度。 相似文献
9.
Victor Wee Lin Ng 《Journal of organometallic chemistry》2005,690(9):2323-2332
The reaction of [CpCr(CO)3]2 (Cp = η5-C5H5) (1) with 1 mol equivalent of 2,5-dimercapto-1,3,4-thiadiazole (DMcTH2) at ambient temperature led to the isolation of a reddish-brown crystalline solid of CpCr(CO)3(η1-DMcTH) (5) and a green solid of CpCr(CO)3H (2) in yields of ca. 28% and 30%, respectively, along with some [CpCr(CO)2]2 (3) and [CpCr(CO)2]2S (4). The reaction of 1 with 1 mol equivalent of vinylene trithiocarbonate (SCS(CH)2S) (VTTC) at 90 °C led to the isolation of a red crystalline solid of CpCr(CO)2(η2-SCHSC2H2) (6) in ca. 15% yield while the reaction of 1 with isopropylxanthic disulfide ((CH3)2CHOCS2)2 resulted in the formation of CpCr(CO)2(η2-S2COCH(CH3)2) (8) in ca. 80% yield. The complexes 5, 6 and 8 have been determined by single crystal X-ray diffraction analysis. 相似文献
10.
Tan BJ Sow CH Koh TS Chin KC Wee AT Ong CK 《The journal of physical chemistry. B》2005,109(22):11100-11109
Two-dimensional ordered arrays of gold (Au) nanoparticles were fabricated using two different variants of the nanosphere lithography technique. First, ordered arrays of polystyrene nanospheres on Si substrate were used as deposition masks through which gold films were deposited by electron beam evaporation. After the removal of the nanospheres, an array of triangular Au nanodisks was left on the Si substrate. After thermal annealing at increasing temperature, systematic shape transition of the nanostructures from original triangular Au nanodisks to rounded nanoparticles was observed. This approach allows us to systematically vary the size and morphology of the particles. In the second and novel technique, we made use of reactive ion etching to simultaneously reduce the dimension of the masking nanospheres and create arrays of nanopores on the substrate prior to the deposition of the Au films. These samples were subsequently annealed, which resulted in size-tunable and ordered Au nanoparticle arrays with the nanoparticles nested in the nanopores of the templated substrate. With the nanoparticles anchored in the nanopores, the substrate could be useful as a template for growth of other nanomaterials. 相似文献